To enhance safety in driving a vehicle, the popularization of a vehicle-mounted camera for observing a situation outside the vehicle such as rear verification and the recognition of a white line accelerates.
In some cases, the vehicle-mounted camera is installed inside a vehicle. However, since it is suitable to install the vehicle-mounted camera outside a vehicle so as to widely monitor an ambient situation, the vehicle-mounted camera is mainly installed outside a vehicle. When the vehicle-mounted camera is installed outside a vehicle, there is a case where it is difficult to grasp an ambient situation because water droplets adhere to a lens of the vehicle-mounted camera because of rainfall, snow coverage and others and scatter light incident on the camera. Therefore, technique for providing a mechanism that jets a clearing solvent onto the lens of the vehicle-mounted camera so as to clean a surface of the lens is disclosed in Patent Literature 1.
In Patent Literature 1, the cleaning device that jets the clearing solvent onto the vehicle-mounted camera is required and the replenishment of the clearing solvent is also required. Therefore, in a vehicle provided with the cleaning device, space for the cleaning device and a clearing solvent tank is required, and wiring for driving the cleaning device and piping for the clearing solvent are also required. Besides, a user who manages the vehicle has to replenish the clearing solvent.
As described above, as the cleaning device that jets the clearing solvent is required to secure space inside the vehicle and further, the user has to replenish the clearing solvent, technique that does not require these has been demanded.
It is considered that as water droplets turn into a water film when the surface of the lens is made hydrophilic, the scatter of light by the water droplets is inhibited and a field of view becomes satisfactory. For a method of making a surface of a lens hydrophilic, a method of forming a titanium dioxide containing film on the surface can be given. However, since the hydrophilic property of titanium dioxide does not emerge when no ultraviolet light irradiates it, its effect is not fulfilled in running at night.
In Patent Literature 2, technique for exerting a hydrophilic property even if no light irradiates is disclosed. This technique uses a film configured by inorganic oxide particles such as silicon dioxide and a void on a surface of a lens.
The inorganic oxide has a higher hydrophilic property in general compared with an organic substance, a glass plate made of silicon dioxide has a smaller contact angle with water, compared with a plate made of acrylic resin and others for example, and has the high hydrophilic property.